Interior permanent magnet machines are used in many different applications, including but not limited to vehicle applications. For example, IPM machines may be used in vehicle alternator-starter systems to provide engine cranking for engine starts and to generate power for vehicle electrical loads. In some vehicles, energy is saved and emissions are reduced by “on-and-off” operation, that is, by turning the engine on and off based on emission and gas consumption levels. Such engines may need repeated starting, for example, during urban stop-and-go operation.
A number of circumstances can affect the performance of an IPM machine during restart, not only in vehicle applications but also in other applications. For example, a fault in a processor controlling an IPM machine could cause the machine to lose synchronization. It is desirable for IPM machines to start up and restart smoothly in such situations.